Corrosion is a major problem in any system in which ferrous metals are in contact with aqueous solutions. Corrosion is the electrochemical reaction of metal with its environment. It is a destructive reaction, which simply stated, is the reversion of refined metals to their natural state. For example, iron ore is iron oxide. Iron oxide is refined into steel. When the steel corrodes, it forms iron oxide which may result in failure or destruction of the metal, causing the particular aqueous system to be shut down until the necessary repairs can be made. Typical systems in which corrosion of ferrous metals is a problem include but are not limited to water based cooling systems, waste water handling systems and systems which transport or process natural gas or crude oil.
Crude oil production provides a good example of the types of systems in which ferrous metal corrosion is a problem. When crude oil is produced from an oil bearing formation the crude oil is commonly mixed with water. The water typically contains dissolved salts and is referred to in the industry as "brine". The brine can become mixed with the crude oil as a result of oil recovery flooding or is a naturally occurring fluid found in the formation from which the crude oil is recovered. One of the first processing steps which the crude oil is subjected to is the separation of the brine from the crude oil. Brine, due to the presence of dissolved salts, particularly MgCl.sub.2 which hydrolyzes to form HCl, is very corrosive to the metal separation equipment and piping which separates the brine and crude oil and which transports the brine back into the environment for disposal. After brine separation, pipelines which transport oil or gas can contain some residual water which can cause corrosion problems in the piping and related equipment.
Another example of the type of system in which ferrous metal corrosion is a problem is in the removal of acid gases (typically CO.sub.2 and/or H.sub.2 S) from crude oil or natural gas. Acid gases are commonly removed in an acid gas removal amine system (amine unit). An amine unit uses an organic amine such as monoethanolamine (MEA), diethanol amine (DEA), methyldiethanolamine (MDEA), diisopropanolamine (DIPA), diglycolamine (DGA) or triethanolamine (TEA) diluted in water as an amine solvent. The amine solvent reacts with the acid gases thereby removing them from the hydrocarbon. The amine-acid gas reaction is later reversed resulting in an acid gas stream and a reusable solvent. Unreacted CO.sub.2 can form carbonic acid which causes metals in the amine unit to corrode.
Efforts to control corrosion in amine units usually focus on the use of metallurgy, minimization of acid gas flashing, filtration, stress relieving and similar mechanical design considerations. Mechanical design considerations, process controls and chemical corrosion inhibitors help reduce corrosion in amine units but do not eliminate the problem.
Since corrosion, if left untreated, can cause shut down of a system, corrosion control is an important consideration in any operations in which ferrous metal contacts water.
Accordingly, a need exists for relatively low toxicity compositions which, when added to an aqueous system, inhibit corrosion of ferrous metals.